which directory data should i remove , so it will start downloading blockchain again ?

/root/.bitcoin/blocks ?/root/.bitcoin/chainstate

You only need to delete /root/.bitcoin/blocks

You might want to delete chainstate (which contain all UTXO) and txindex (which contain all transaction index) folder as well since both of them will be recreated anyway and just in case if those two are corrupted as well.

which directory data should i remove , so it will start downloading blockchain again ?

/root/.bitcoin/blocks ?/root/.bitcoin/chainstate

You only need to delete /root/.bitcoin/blocks

You might want to delete chainstate (which contain all UTXO) and txindex (which contain all transaction index) folder as well since both of them will be recreated anyway and just in case if those two are corrupted as well.